Electrical discharge device



1933. 'r. E, F-OULKE 1,930,083

ELECTRICAL DI SCI-IARGE DEVICE Filed Jan. 5, 1929 Y I v; I I

H l5 ATTORNEY Patented Oct. 10, 1933 PATENT OFFICE ELECTRICAL DISCHARGE DEVICE Ted Eugene Foulke, Nutley, N. 1., assignor to General Electric Vapor Lamp Company, Hoboken, N. J., a corporation of New Jersey Application January 3, 1929. Serial No. 330,117

4 Claims.

The present invention relates to electrical discharge devices, useful in the arts generally, as indicator lamps, for example, and particularly useful as lightning arresters.

The particular object of the invention is to provide a gaseous electric discharge device which will have the desired characteristics of maintaining its rated breakdown potential througli'cut its entire life, after repeated cycles of operation, as a lightning arrester, for example, and which will be rugged in construction and one having its electrodes so constructed as to resist displacement or breaking off, and thus avoiding distortion of the desired fixed relation of the various parts of the device, which distortion would cause deleterious disturbances in the device itself as well as in other circuits with which the device is connected and which it is designed to protect.

Another object is to eliminate the time lag before discharge is started which is inherent in such devices. Other objects will be apparent from the following specification or from an inspection of the drawing.

iii)

The invention consists of a new and novel combination of elements, as hereinafter set forth and claimed.

For purposes of illustration one embodiment of the invention is shown in the accompanying drawing, in which Fig. 1 is a longitudinal cross section of a lightning arrester,

Fig. 2 is a sectional view taken at the line 2-2 of Fig. 1, v

Fig. 3 is a view of the electrode structure at one.

stage of its manufacture.

Figs. 4 and 5 are respectively end and side views of an insulator used in the device, and

" Fig. 6 is a view of the in-lead.

In the drawing an envelope 1 of glass or other suitable material contains a suitable gas and has sealed thereinto at opposite ends the in-leads 2 of dumet or other metal suitable for sealing-in purposes. Over the inner end of each in-lead, which is bent to give better support therefor, is crimped a pointed metal terminal 3, which may be made from sheet metal as shown in Fig. 3. Between the electrodes 3 and the re-entrant seals 4 are placed bushings 5 of lavite, porcelain, or other suitable insulating material, for confining the discharge to the electrodes 3. The bushings 5 combe subjected is provided in the form of a substance 6 such as DeKhotinsky cement, sealing wax, or similar material, which fills the space around inleads 2 within the re-entrant seals 4. An equivalent structure would be a ferrule which would fitsnugly upon the end of the envelope 1, with a suitable opening therein for the in-lead 2.

The insulating bushings 5 are designed to completely shield the lead-in 2 between the electrode 3 and the seal 4 from any possible discharge, since a discharge at this point would tend to crack the seal, or due to the small thermal capacity of the in-lead 2 this wire might be fused. The electrodes 3 are also designedwith considerable heat capacity in order to keep their operating temperature as low as possible.

The gap between the pointed ends of electrodes short circuiting the device, as in some instances serious trouble may be caused in the associated circuits if the starting and operating characteristic of the arrester becomes altered for any reason.

The electrodes are preferably free of occluded gases and iron has been found to'be a suitable electrode material. In order to prevent oxidation of the iron during the sealing in process it is preferably plated with nickel, chromium, :cobalt, or other metals which do not readily oxidize.

The gas filling consists of one of therare gases, or a mixture thereof in proportions to give the desired breakdown potential. For example with the gap between the electrodes 3 about one half inch in length either a mixture of neon with a small percentage (less than .5% and greater. than .1%) of argon, or a mixture of 30% helium, approximately neon, and the same quantity of argon as before, will give a breakdown potential on the order of 100 to 200 volts, when the gas pressure is about 45 mm of mercury. To control this breakdown potential either the gap between the electrodes, the pressure of the gas, 'or the character of the gas filling may be varied. Preferably the latter two are the conditions which are changed. With a one half inch gap between the electrodes 3 the following table sets forth several preferred variations:

For other ranges up to 1000 volts or more pure argon is used at pressures proportionately greater.

In order to insure a constant breakdown potential throughout the life of the device it is important that all occluded gases be driven oil? from the electrode during manufacture, in order that no gas remains to be driven off during discharge. The preferred method for accomplishing this is to fire the iron electrode, prior to plating, in hydrogen at a temperature of about 1100" C. whereby all the occluded gases are displaced by hydrogen, as is well known in the art. This hydrogen is later driven off while the discharge device in which it has been incorporated is being evacuated by placing the device within the influence of a high frequency magnetic field whereby the electrode is raised to a high temperature while a vacuum is maintained.

Heretofore all low pressure types of arresters have had appreciable time lags on waves with steep wave fronts as compared to sinusoidal waves of lower frequency. For example, a gaseous discharge type arrester such as above described when used in connection with 1,000,000 cycles,

, such as may be encountered in lightning diacharges, would require a voltage of the order of ten times the rated breakdown voltage at cycles. This condition has been especially noticeable when the device has been shielded in any way by means of a metal casing, as in the mounting. It has been discovered that this lag may be overcome by the use of a discharge starting material such as radium chloride or other suitable compound of radium, uranium, thorium, or other alpha ray emitting substances, which may be placed on an electrode or incorporated in the glass of the container 1, in combination with a small quantity of an alkali metal, such as rubidium or caesium. These may be located at any point adjacent to the electrodes, but are most conveniently applied thereto. Either one of these discharge starting additions will improve the action of the device, but two of them in combination, as, for example, radium chloride and rubidium, will completely eliminate the lag. In the presence of these elements the time lag is cut to a value commensurate with that obtained with a 4 mil gap in air, which is considered one of the fastest operating gaps known. And a discharge device constructed with these materials present will be found to retain its high speed characteristics regardless of shielding. The most convenient way in which to apply the-radium chloride and the alkali metal, for instance, is to dip one or both of the electrodes 3 into a bath in which the radium chloride and the azide of the alkali metal chosen are present. During the later heat treatment of the electrode, during evacuation, the azide will be reduced, leaving the desired pure metal.

While the electrodes 3 have been shown as made of sheet metal, an obvious alternative would be to turn them from rod stock, with a hole in the center into which the bent end of the in-lead 2 could be inserted, the electrode then being subjected to pressure to flow the metal of the electrode around said in-lead, making the very solid connection, or the in-lead 2 can be welded or threaded into said electrode 3.

The devices of my invention, in operation. have been found to be most eiiicient as they will withstand repeated heavy current surges in protection systems without disintegration of the device itself and without change of the fixed operating characteristics thereof, resulting in constant functioning of the device for a long life and requiring a minimum of inspection service.

It is to be understood that the various proportions, pressures, materials and the like which have been herein indicated are typical and have been given for purposes of illustration only since my invention is not limited thereto.

I claim:

1. A lightning arrester comprising in combination, an envelope; a gaseous atmosphere therein at a pressure of the order of 25-45 mm. of mercury, spaced apart electrodes therein, radium in said envelope and rubidium on at least one of said electrodes.

2. A lightning arrester comprising in combination, an envelope, electrodes therein, a gaseous atmosphere in said envelope at a pressure of the order of 25-45 mm. 01' mercury, and a radioactive substance and an alkali metal within said envelope.

3. A lightning arrester comprising in combination, an envelope, electrodes therein, said electrodes being free of occluded gas, a gaseous atmosphere at a pressure of the order of 25-45 mm. of mercury in said envelope, and a radioactive substance and an alkali metal within said envelope.

.4. The method of making a gaseous discharge device comprising forming electrodes of iron, 11ring said electrodes in hydrogen at a high temperature, coating said electrodes with an oxidation resisting metal, applying a radioactive substance and an alkali metal to said electrodes, sealing said electrodes into a container, heating said electrodes in vacuum by means of a high frequency magnetic field, and providing a suitable gaseous atmosphere about said electrodes.

TED EUGENE FOULKE. 

